In wireless systems, such as multiple input multiple output (MIMO) wireless systems, for example, multiple antennas are used on both the base station and on the mobile device to exploit a phenomenon known as multipath propagation in order to achieve higher data rates. In general, wireless systems such as MIMO systems simultaneously send and receive multiple data signals over each radio channel. The multipath propagation phenomenon is the result of environmental factors that influence the data signals as they travel between the base station and the mobile device, including, for example, ionospheric reflection and refraction, atmospheric ducting, reflection from terrestrial objects and reflection from bodies of water. Because of these factors, the data signals experience multipath interference that results in constructive interference, destructive interference, or fading, and phase shifting of the data signals. MIMO technology has been standardized in various wireless communications standards including Institute of Electrical and Electronics Engineers (IEEE) 802.11n, IEEE 802.11ac, HSPA+ (3G), WiMAX (4G) and Long Term Evolution (LTE) standards.
Base stations and mobile devices of wireless systems require testing. A typical test system for testing a mobile device under test (DUT) includes a base station or base station emulator (BS), a radio channel (RC), or fading, emulator, the mobile device under test (DUT), a personal computer (PC), some type of multi-probe configuration, and various electrical cables for interconnecting the components. This same test system configuration can be used to test the BS when the BS is the DUT. In some test systems, the output ports of the fading emulator are connected to the antenna ports of the DUT by electrical cables. This type of test system is known as a conducted test system.
Another type of test system that is used to test mobile DUTs is a multi-probe anechoic chamber (MPAC) over-the-air (OTA) test system. In a typical MPAC OTA system, the mobile DUT is located inside of an anechoic chamber that includes a multi-antenna probe configuration. The output ports of the fading emulator are connected to the respective antenna probes of the chamber. This same test system configuration can be used to test the BS when the BS is the DUT.
The latest generation of wireless systems is the 5th generation wireless system, commonly abbreviated as “5G.” It is expected that 5G wireless systems that operate in the millimeter wave spectrum (mmWave), which is between 30 GHz and 300 GHz, will employ integrated analog beamforming with fast dynamic beam switching in both the BS and the user equipment (UE) (e.g., a mobile device). It is not expected that analog beamformers will be applied at frequencies below 6 GHz, although the current signaling specification draft does not preclude it. For 5G wireless systems, OTA test methods and systems will be used to test the BS and the UE if RF antenna connectors at each antenna element are not available. It is expected that connectors for conductive radio channel emulation will be available at RF or intermediate frequency (IF) on an antenna port basis rather than on a per antenna element basis. Each antenna port will be connected to multiple antenna elements and analog beamforming with a fixed set of element weighting coefficients will be applied at each antenna port such that a different beam state may be chosen for each orthogonal frequency division multiplexing (OFDM) symbol.
A need exists for an MPAC OTA test system that can be used to test 5G BSs and 5G UEs. A further need exists for an MPAC OTA test system that can be used to test 5G BSs and 5G UEs that reduces the amount of RC emulator resources that are needed in the RC emulator and that reduces the number of antenna probes that are needed in the anechoic chamber in order to reduce the complexity and cost of the MPAC OTA test system.